Currently, one of the most difficult portions of the human to repair and to protect during healing is the spinal column or spine. In simple terms, the spine may be viewed as a series of vertebrae connected by and alternating with intersticial positioned spinal discs. The spinal discs include an outer portion referred to as an annulus formed of relatively tough and only minimally elastic material that is, nonetheless, pliable and may be likened to leather. Each annulus surrounds a nucleus that is constituted from a highly viscous gel-type material. Each annulus is secured with a superior vertebra across a bony endplate of the vertebra, as well as an inferior vertebra across a bony endplate of the inferior vertebra.
Each vertebra has a channel for the spinal nerve separated from endplates and discs. The discs support and enable the biomechanical movement of the torso, such as flexion/extension in anterior, posterior, and lateral directions, and in torsional movement around a general vertical axis of the spine.
Should one or more discs be damaged, a person may experience pain from a number of the modes. In one mode, the annulus may be damaged so that the disc bulges and presses on the spinal nerve. In another mode, the annulus may fail to provide sufficient support so that the portion of the spine in a superior position to the damaged annulus compress downwardly, which also compresses the spinal nerve. Another mode is a damaged vertebra that results in pain or contributes to damage of portions of the spine.
A number of treatments are known for addressing spinal pain and other conditions (such as scoliosis or other unfortunate but naturally occurring conditions). While there are non-surgical treatments available for some pain originating from damage to the spinal column, such are typically limited to minor irregularities. For any significant damage, surgical procedures are often necessary to relieve pain and/or regain a portion of a person's mobility.
One category of such procedures is defined by the use of intervertebral implants. Intervertebral implants specifically are devices that are placed in the interstice that normally is occupied only by the naturally occurring spinal disc. Intervertebral implants may be total disc replacements (TDR) following a discectomy, removal of the entirety of the naturally occurring disc. Other intervertebral implants are intradiscal wherein a portion or entirety of the nucleus is removed (a procedure known as a nucleotomy) and replaced with one or more implants within the natural annulus. Some known implants designs, whether TDR or intradiscal, are designed to mimic or replace the natural biomechanical properties of the natural disc, while others are fusion discs seeking to immobilize the superior and inferior vertebrae, generally permanently. For fusion implants, it is known to design implants and perform procedures that seek to stimulate, promote, or benefit from bone in-growth into the intervertebral space, implants that may or may not include natural or artificial bone graft material.
There are a number of difficulties with current designs and procedures for locating and implanting the variety of intervertebral implants. To begin with, a common manner for implantation requires a distractor device applied to adjacent vertebrae. This is necessary, since the diseased disc space is typically very narrow, and collapsed. This disc space height must be restored if an optimal outcome is to be achieved. Replacing the support provided by the disc requires spanning the distance between the endplates, which have concave surfaces facing the disc. Therefore, the distance between the vertebrae at the outer portion of the nucleus is smaller than the desired height for the implant construct. Applying a distractor to the vertebrae assists in forcing the larger implant between the vertebrae.
One example of a prior art implantation device or insertion distractor is shown in U.S. Pat. No. 3,486,505, to Morrison. This '505 patent requires placing distal portions of opposed arms between adjacent vertebrae. Once there, a plunger or rod is advanced to force an implant between the arms, thereby spreading the arms and distal portions thereof outwardly to distract the vertebrae. This method and design puts a significant amount of stress on the implant itself, as it is the implant that is doing much of the work. Such compression may damage the implant before the implant is ever disposed in the intervertebral space, and high frictional forces are exerted on the sides of the implant that are in contact with the arms. Finally, as the implant is doing the work, manipulation of the implant to a desired purpose is hindered, particularly once the implant has passed beyond the arm distal portions so that it is in full and direct contact with the endplates.
While the design of the '505 needs the implant to slide, generally prevents use with an implant having surface fixation features such as spikes, U.S. Patent Application Publication No. 2008/0161817, to Parsons, et al. attempts to overcome such deficiency. Specifically, the implant has laterally located spikes, the arms of the inserter device engaging on a central portion of the implant with the spikes positioned outboard therefrom. Additionally, the plunger itself appears to provide at least a part of the distraction force for the arms. However, the '817 design maintains the spikes in an exposed position at all times during implantation. Additionally, the implant must be located between the arms at the distal end of the distractor/implantor device prior to placing the device in situ, resulting in the spikes being exposed and seating of the implant being susceptible to being effected during the preliminary steps of interfacing the distractor device with the vertebrae.
U.S. Pat. No. 6,368,325, to McKinley, et al., describes a distractor/implantor device specifically described for use with bone blocks. The device includes an elongated handle with a distal forked end defining a space for receiving a bone block therein. The leading surfaces of the fork tines are beveled and, in particular, are shown as having a bevel that aligns with a bevel surface formed on a leading end of the bone block protruding from between the tines. The bevel surfaces are used to initially wedge first the bone block, then the tines between the vertebrae, a major dimension extending laterally and a minor dimension extending in the spinal superior-inferior (rostral-caudal) direction. The entirety of the device is then rotated around its generally longitudinal axis to distract the vertebrae, the major axis being aligned with the superior-inferior direction. A central rod is then advanced to eject the bone block.
The design of the '325 patent overcomes some of the deficiencies of the above-discussed references, while still presenting other deficiencies. For instance, none of the devices permits selection of an implant device after distraction has occurred. A surgeon may desire to inspect and size the intradiscal or intervertebral space prior to selecting the implant. The above-discussed devices do not permit such inspection without sequential insertion and removal of the distractor/implantor device, or another device (such as a sizer or spacer). Similarly, none of the devices discussed herein allows for sequentially implanting a plurality of implant constructs, or components thereof. The '325 patent also relies on compression directly on the implant during insertion and rotation of the device. The major benefit of the design of the '325 patent is that, once the device is rotated and the vertebrae are distracted, the implant itself can relatively easily be advanced from the device without further distraction.
Another design for a distractor/implantor is illustrated by U.S. Patent Application Publication No. 2007/0270875, to Bacher, et al. Essentially, a central rod pointed tip is utilized as an initial distractor, an outer sleeve has fingers that form a frusto-conical portion extending from the rod pointed tip, and an inner sleeve receives the central rod while itself being received by the outer sleeve. While various uses of the illustrated device may be imagined, one minimally requires the inner and outer sleeves to remain between the vertebrae during distraction and implantation.
Accordingly, there has been a need for an improved distractor/implantor device for locating and implanting artificial spinal discs in intervertebral spaces.